REVISED POURBAIX DIAGRAMS FOR ZINC AT 25-300-DEGREES-C

Pourbaix diagrams (potential/pH diagrams) for zinc at 25-300 degrees C have been revised. The diagrams were calculated for three concentrati ons, 10(-5), 10(-6) and 10(-8) molal, the latter for use in high purit y water such as in nuclear power reactors. Extrapolation of thermochem ical data to elevated temperatures has been performed with the revised model of Helgeson-Kirkham-Flowers, which also allows uncharged aqueou s complexes, such as Zn(OH)(2)(aq), to be handled. The calculations sh ow that the hydroxide of zinc does not passivate at the concentration of 10(-6) M, due to the uncharged zinc(II) complex, Zn(OH)2(aq). Howev er, at concentrations greater than or equal to 10(-5.7) M zinc passiva tes by formation of ZnO, which is stable in the temperature interval i nvestigated. Copyright (C) 1996 Elsevier Science Ltd